I guess I was kinda greedy on this one, or was I? Opponent is fish 32 hands, 50/28, Aggro, 55% WTSD.

His raise on the turn and bet near full pot on the river suggested he had a strong hand (set, 2 pair, AQ). That's why I tried to put him AI, because I thought he would call any bet with a very strong hand and if he was bluffing he wouldn't pay off any raise.

On the other hand, my straight isn't too well hidden, it's kinda obvious any 6 would have a straight, but can fish see these things?

Well, I don't like the idea of betting even that smallish on turn.
If you want to bet it then make it properly. Also as played I'd rather give up my hand. We don't get god implied odds there anyways. While we could be already vs 67! And are drawing for pretty much nothing.

As played pretty much overplayed your hand.
Doubt that you are getting called by a lot worse anyways. And might at the best just split the pot vs another 6x. I might even prefer donking myself there to avoid them Checking behind on such a board which is even very likely.